By Keith S. Wexler, MBA, Maternal Fetal Medicine, Prenatal Diagnosis and Biotech/Life Sciences Consultant, GENASSIST, Inc.
Paul Wexler, M.D., F.A.C.O.G., Medical Director, GENASSIST, Inc.
Clinical Professor, Department of OB/GYN, University of Colorado Health Sciences Center
Clinical Professor, Division of Genetics/Dept. of Pediatrics, Univ. of Colorado/The Children’s Hospital
Background: Fetal DNA believed released from the placental trophoblasts circulating in the maternal circulation make it possible for laboratories to screen for Fetal DNA during pregnancy. Fetal DNA represents approximately 10-14% of Cell Free DNA in the maternal circulation.
This prenatal non-invasive testing can be performed as early as the 10th week of pregnancy.
Maternal Fetal Circulating Cell Free DNA (cf DNA) has helped uncover microdeletions – losses of very small pieces of chromosome(s) that are not visible under a microscope and can be associated with syndromes in a child.
Angelman Syndrome: Is a specific type of severe developmental delay where a patient may have balance and/or walking problems.
This type of developmental delay is caused by a loss of a small portion of the long arm of chromosome #15 (15q21) or two copies of paternal chromosomes #15 and no maternal chromosome #15 (Uniparental Isodisomy).
- Incidence – 1 in 12,000 to 1 in 20,000 births.
Prior to Maternal Fetal DNA screening tests in pregnancy, the only way a patient would know if they had a child with a microdeletion was at delivery with an “affected” child.
At the current time the value of “routine” screening for Microdeletions on all patients is controversial because of the low prevalence of these disorders and the possibility of “false positive” and “false negative” results.
However, when a patient is identified as a candidate for invasive testing i.e. Chorionic Villus Sampling (CVS) and/or amniocentesis, the addition of Microdeletions may be indicated, particularly if family history or ultrasound findings suggest an increased possibility for detection of one of these rare disorders.